Adding Hooks

    • Global HTTP hooks HTTP transaction hooks are set on a global basis using the function . This means that the continuation specified as the parameter to TSHttpHookAdd is called for every transaction. TSHttpHookAdd must be used in TSPluginInit.
    • Transformation hooks Transformation hooks are a special case of transaction hooks. See TSVConnCacheObjectSizeGet() for more information about transformation hooks. You add a transformation hook using TSHttpTxnHookAdd, as described in .
    • HTTP select alternate hook Alternate selection hooks enable you to hook on to the alternate selection state. These hooks must be added globally, since Traffic Server does not have a handle to a transaction or session when alternate selection is taking place. See HTTP Alternate Selection for information on the alternate selection mechanism.

    All of the hook addition functions (, TSHttpSsnHookAdd(), ) take TSHttpHookID (identifies the hook to add on to) and TSCont (the basic callback mechanism in Traffic Server). A single TSCont can be added to any number of hooks at a time.

    An HTTP hook is identified by the enumerated type TSHttpHookID. The values for are:

    Values for TSHttpHookID

    TS_HTTP_CACHE_LOOKUP_COMPLETE_HOOK

    Called after the HTTP state machine has completed the cache lookup for the document requested in the ongoing transaction. Register this hook via TSHttpTxnHookAdd or TSHttpHookAdd. Corresponds to the event TS_EVENT_HTTP_CACHE_LOOKUP_COMPLETE.

    TS_HTTP_OS_DNS_HOOK

    Called immediately after the HTTP state machine has completed a DNS lookup of the origin server. The HTTP state machine will know the origin server’s IP address at this point, which is useful for performing both authentication and blacklisting. Corresponds to the event TS_EVENT_HTTP_OS_DNS.

    TS_HTTP_POST_REMAP_HOOK

    Called immediately after remapping occurs, before cache lookup. Corresponds to the event TS_EVENT_HTTP_POST_REMAP.

    TS_HTTP_PRE_REMAP_HOOK

    Called after the request header is read from the client, before any remapping of the headers occurs. Corresponds to the event TS_EVENT_HTTP_PRE_REMAP.

    TS_HTTP_READ_CACHE_HDR_HOOK

    TS_HTTP_READ_RESPONSE_HDR_HOOK

    Called immediately after the response header is read from the origin server or parent proxy. Corresponds to the event .

    TS_HTTP_RESPONSE_TRANSFORM_HOOK

    See “Transformations” for information about transformation hooks.

    TS_HTTP_READ_REQUEST_HDR_HOOK

    Called immediately after the request header is read from the client. Corresponds to the event TS_EVENT_HTTP_READ_REQUEST_HDR.

    TS_HTTP_REQUEST_TRANSFORM_HOOK

    See for information about transformation hooks.

    TS_HTTP_SELECT_ALT_HOOK

    See “HTTP Alternate Selection” for information about the alternate selection mechanism.

    TS_HTTP_SEND_RESPONSE_HDR_HOOK

    Called immediately before the proxy’s response header is written to the client; this hook is usually used for modifying the response header. Corresponds to the event TS_EVENT_HTTP_SEND_RESPONSE_HDR.

    Called immediately before the proxy’s request header is sent to the origin server or the parent proxy. This hook is not called if the document is being served from cache. This hook is usually used for modifying the proxy’s request header before it is sent to the origin server or parent proxy.

    Caution

    TS_HTTP_SEND_REQUEST_HDR_HOOK may callback several times when the OS crashed. Be careful to use functions such as TSContDestroy in TS_HTTP_SEND_REQUEST_HDR_HOOK hook.

    TS_HTTP_SSN_CLOSE_HOOK

    Called when an HTTP session ends. A session ends when the client connection is closed. You can only add this hook as a global hook

    TS_HTTP_SSN_START_HOOK

    Called when an HTTP session is started. A session starts when a client connects to Traffic Server. You can only add this hook as a global hook.

    TS_HTTP_TXN_CLOSE_HOOK

    Called when an HTTP transaction ends.

    TS_HTTP_TXN_START_HOOK

    Called when an HTTP transaction is started. A transaction starts when either a client connects to Traffic Server and data is available on the connection, or a previous client connection that was left open for keep alive has new data available.

    The function you use to add a global HTTP hook is .